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SleepUncovered

Cortisol and sleep — the morning hormone

Updated16 May 2026Read time5 minReviewed bySleepUncovered editorial

Short answer

Strong evidence

Cortisol is the body's primary alertness and stress hormone. It follows a sharp circadian rhythm: lowest around midnight, rising in the last hours of sleep, peaking 30–45 minutes after wake, then declining through the day. When this rhythm flattens or spikes at the wrong time, sleep breaks — particularly middle-of-night waking.

Key points

  • The cortisol awakening response (CAR) is the morning peak — a 50–100% rise above baseline in the first 30–45 minutes after waking.
  • Cortisol falls steadily through the day, reaching its nadir around midnight.
  • Chronic stress, depression, and shift work flatten the rhythm — high evening cortisol fragments sleep.
  • Late-night cortisol spikes (from work, news, conflict, alcohol metabolism) commonly cause 2–4am wake-ups.
  • Adequate morning light, consistent wake time, and managing evening arousal protect the rhythm.

The normal rhythm

Cortisol is produced by the adrenal glands under control of the HPA (hypothalamic-pituitary-adrenal) axis. Its release follows a strict circadian pattern in healthy adults:

  • Lowest around midnight (the “cortisol nadir”).
  • Rises gradually through the last 2–3 hours of sleep.
  • Spikes 50–100% in the first 30–45 minutes after waking — the cortisol awakening response.
  • Declines steadily through the day with smaller peaks at meals.

This isn't a stress response. It's a normal, healthy signal that promotes morning alertness and helps mobilise energy. Without it, you'd feel groggy for hours after waking.

What flattens the rhythm

Chronic stress, depression, burnout, shift work, and several medical conditions can flatten the cortisol curve — producing less morning peak and more evening cortisol. The shape of the curve, not just the total cortisol, is what matters.

A flat cortisol rhythm is associated with worse sleep, fatigue, mood disturbance, and metabolic dysregulation. Treating the underlying cause (stress, depression, sleep disorder) usually restores the rhythm; cortisol-targeting interventions in isolation rarely help.

Late-night cortisol spikes

The 3am-wide-awake-and-alert pattern usually has cortisol behind it. Triggers include:

  • Alcohol metabolism in the second half of the night — cortisol rises as blood alcohol falls.
  • Late work or stressful content within 2 hours of bed.
  • Low blood sugar overnight — the body compensates by raising cortisol to mobilise glucose.
  • Anxiety, particularly when worrying about not sleeping (cortisol responds to anticipation).

Protecting the rhythm

  • Morning light exposure — the single biggest lever for a healthy cortisol peak.
  • Consistent wake time — irregular wake times flatten the morning peak.
  • Wind down 1–2 hours before bed — dim light, calm content, no work email.
  • Treat underlying stress or depression rather than cortisol directly.

About cortisol supplements and tests

Salivary cortisol panels are marketed for self-diagnosis. Used well, they can show flatness or inversion in clinical settings. Used casually, they often produce false alarms — cortisol fluctuates significantly day-to-day. If you suspect a real problem, a clinician interpreting a properly-timed panel is the right route.

Adaptogens (ashwagandha, rhodiola) marketed to lower cortisol have small effects in stressed populations. The bigger lever is reducing the inputs that drive cortisol up in the first place.

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